The present invention relates to flow cells generally, and more particularly to radiant energy flow cells for use in various analytical chemistry applications, such as spectrophotometry. This invention also relates to methods for fabricating such flow cells.
Numerous devices have been designed and implemented for use in preparing and testing samples in various environments, particularly in analytical chemistry applications. One such device is a flow cell, which may be used to transport samples to and through analytical instruments such as spectrophotometers for analysis purposes. Flow cells have typically been utilized to transport liquid samples, but other flowable sample types have also been implemented.
Most commonly, flow cells have been implemented to transport sample solutions through a volume disposed between a radiant energy source and an energy detector, which detector measures the relevant energy absorption or transmission through the sample solution. An example of such a detector is a spectrophotometer. Various analytical instruments then interpret the resultant energy xe2x80x9cfingerprintsxe2x80x9d or transmitted vs. absorbed wavelengths to decipher sample constituents.
To efficiently pass the energy through the sample solution, however, the flow cell walls typically use focusing optics such that energy impact upon the flow cell walls is minimized. Without such focusing optics, previous flow cell configurations called for the sample solvating fluid to have a higher index of refraction than materials commonly used in the flow cell walls. As a result, organic fluids were typically utilized as solvents in flow cell applications prior to the incorporation of focusing optics.
For several reasons, however, aqueous fluid carriers have been sought as a preferred alternative to such organic fluids. To implement a flow cell system utilizing an aqueous fluid, a material having an index of refraction less than that of water is needed for the respective flow cells. One such material is a perflourinated copolymer developed by DuPont of Wilmington, Del., under the trade name Teflon AF(trademark). Thus, analytical flow cells preferably include a layer of Teflon AF(trademark) or other low index of refraction material to allow efficient radiant energy propagation in spectrophotometry and photometry applications.
An additional issue encountered by current flow cell systems is the transmission of stray light through the cell to a photometric detector downstream therefrom. Generally speaking, stray light is light which is perceived by the photometric detector without first passing through the sample being analyzed. Such stray light is most often a result of light transmitting directly through transparent or translucent flow cell material without passing through the sample path. As stated above, flow cell systems are specifically designed to maximize internal reflection of photometric radiation through the flow cell to the detector. Such systems simultaneously attempt to minimize source light from entering directly into an end of the flow cell wall to correspondingly minimize stray light reaching the detector. On large scale systems, mechanical photomasking devices have been implemented to block at least incoming light from entering an end of the flow cell wall. As flow cell systems become ever smaller, however, such mechanical photomasking devices become extremely difficult to effectively block stray light while allowing sample radiant energy transmission to pass therethrough into the core of the flow cell.
Most flow cells in use today generally do not embody efficient and reliable designs. Many employ multi-sectional, multi-directional tubes which may cause xe2x80x9cdead flowxe2x80x9d zones, and may introduce an increased risk of fluid leakage. Other flow cell designs are undesirably complex, are difficult to implement in current analytical instrument geometries, or are excessively expensive to produce.
Accordingly, it is a principle object of the present invention to provide an improved means for exposing a sample solution to a radiant energy field used for analyzing sample composition.
It is a further object of the present invention to provide an improved flow cell design yielding desired sample solution flow characteristics.
It is another object of the present invention to provide a flared-tube flow cell design which reduces flow turbulence through the flow cell.
It is a yet further object of the present invention to provide a flow cell having a calibrated gap volume for standardizing radiant energy losses among various fluids flowing through a radiant energy field.
It is a still further object of the present invention to provide an improved flow cell including an end cap having a substantially conical frustum portion which engages the flow cell to form a sealed fluid passageway.
It is a further object of the present invention to provide an improved flow cell having end caps which are sized and configured to form high-pressure fluid seals when engaged with a flow cell body.
It is a yet further object of the present invention to provide end caps for a flow cell, wherein the end caps include passageways for fluid and radiant energy transport, and improved sealing means for sealing relationship with the flow cell.
It is a yet further object of the present invention to provide a flow cell having improved radiant energy transmission characteristics.
It is another object of the present invention to provide a flow cell having improved photomasking characteristics for minimizing or eliminating stray light received by the detector.
It is a further object of the present invention to provide a flow cell having partially opaque walls for minimizing stray light transmission through such walls.
It is a still further object of the present invention to provide an improved flow cell for use in HPLC applications.
It is a yet further object of the present invention to provide a method for fabricating flow cells having improved sealing and fluid transport characteristics.
It is a further object of the present invention to provide a method for fabricating flow cells utilizing extruded tubing.
By means of the present invention, an improved flow cell is contemplated for use in transporting sample fluids in radiant energy fields. Such a flow cell introduces a structure for improved fluid sealing and fluid flow characteristics.
One embodiment of the flow cell of the present invention preferably includes a cell structure having a first elongated tube disposed therein which forms a continuous passageway through the cell structure. The tube includes a radiant energy-blocking portion integral therewith for minimizing passage of stray light through the tube. Attached to the flow cell is at least one end cap that is sealingly engagable with the cell structure. The end cap preferably includes a substantially conical frustum portion extending outwardly therefrom. When assembled, the conical frustum portion preferably extends at least partially into the first open channel.
A first open channel within the first tube is preferably clad with one or more layers forming concentric tubes. Preferably, the innermost tube is a low index of refraction material such as perfluorinated copolymer. A second tube preferably comprising PEEK substantially concentrically surrounds the first tube. Preferably, a third tube comprising FEP substantially concentrically surrounds the PEEK tube, and is in intimate contact with an outer wall of the first open channel. As assembled, the conical frustum portion of the end caps preferably displace a portion of the FEP tube against the first open channel wall, thereby forming a fluid-tight seal between the FEP tube and the conical frustum portions.
Preferably, the end caps include one or more open channels for transporting the sample fluid and the radiant energy. In preferred embodiments, the radiant energy channels are in substantial alignment with the first open channel within the cell structure. The radiant energy channels and the fluid channels preferably merge such that the radiant energy may pass through the sample fluid.
At least one end of the innermost tube is preferably flared outwardly to more efficiently transport the radiant energy and sample fluid. The flared portion of the innermost tube is calibrated so that an internal dimension of the innermost tube may be reduced without significant radiant energy losses, and further enables a reduction in fluid flow turbulence. Such reduced flow turbulence increases the reliability of photometric sample analysis.
In another aspect of the present invention, a gap volume is provided between the first open channel within the cell structure and fluid channels within respective end caps. The gap volume is preferably and adjustably calibrated to define an appropriate volume such that radiant energy losses among various fluids having distinct indexes of refraction may be standardized.
The present invention also contemplates a method for determining sample composition through radiant energy interaction with the sample fluid utilizing the structural elements described above.